This invention relates to shape memory alloys which are transiently or semipermanently usable in almost every part of human.
The Ti (titanium)/Ni (nickel) alloy (Nitinol) has been transiently or semipermanently employed in almost every part of human as a shape memory alloy or a superelastic alloy for biological use. In recent years, however, there arises a problem of a human Ni allergy, especially in European countries. Use of the Ti/Ni alloy would be prohibited before long from the viewpoint of biocompatibility. Accordingly, it has been required to provide a shape memory alloy free from elements which are toxic or allergic to human.
FIG. 1 summarizes the cell growth coefficients of chick embryo myocardial fibroblast and relative cell proliferation ratios of mouse fibroblast-origin L929 cells concerning various pure metals. These data indicate that V, Cd, Co, Cu, Zn, Hg, Al, Cr, etc. have strong cytotoxicity, while Zr, Ti, Nb, Ta, Pt, Au, etc. are excellent in biocompatibility. FIG. 2 shows a relationship between polarization resistance, which serves as an indication of corrosion resistance in vivo, and biocompatibility. As FIG. 2 shows, Pt, Ta, Nb, Ti and Zr are excellent in biocompatibility.
As discussed above, the Ti/Ni alloy has been almost exclusively employed as a shape memory alloy for biological use. As there arises a fear for the serious allergy to Ni, Ni-free shape memory alloys have attracted public attention. On the other hand, Baker and Ahmend et al. reported Ti alloys, but the Ti alloys reported by them are not satisfactory as a shape-memory alloys for biological use.
Under these circumstances, the inventors have made extensive studies to provide Ti alloys having highly biocompatible elements and preferably having the shape memory effects for biological use, and found that a ternary alloy containing Sn as the third element can be a non-toxic and non-allergic alloy having an appropriate shape memory property for biological use. The present invention was accomplished based on this finding.
The alloy according to the present invention is an alloy material comprising (1) Sn (tin), (2) at least one of Ti (titanium) and Zr (zirconium), (3) and at least one of Nb (niobium) and Ta (tantalum).
The present invention also provides a orthodontic appliances, an artificial dental implant, an artificial arthrosis, a born material, a born fixator, a thrombus inhibitor, a catheter introducer, and a Harrington bar comprising the said alloy.